Analysis of ionicity parameters and photoelastic behaviour of AB type crystals

Values of ionicity parameters have been obtained using the revised energy gap model due to Grimes and Cowley. We have used a power law as well as an exponential law for representing the dependences of homopolar energies on interatomic distances. Values of fractional ionic character of the chemical bond are calculated in 68 A^NB^8–N type diatomic solids. The heteropolar energy parameters have been found to exhibit systematic relationships with the interatomic separations for diatomic solids with the common cations in I–VII and II–VI crystals. The strain derivatives of electronic dielectric constant related to the photoelastic behaviour of solids have also been studied with the help of the ionicity parameters within the framework of Phillips–van Vechten dielectric theory. The results obtained from the power law and the exponential law are in close agreement with each other.